Photographic elements



Jan. 12, 1960 R. N. HUOT 2,920,962

PHOTOGRAPHIC ELEMENTS Filed Jan. 10, 1958 400mg, 500 m); 600-mg 700mg Eig.2-

400mg 500m]; 600mg 700mp.

Iii (5.3

400mg 500 my, 600 my, 700mg.

INVENTOR RAYMOND NORMAND HUOT ATTORNEY United States Patent PHOTOGRAPHIC ELEMENTS Raymond Normand Huot, Middletown, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application January 10, 1958, Serial No. 708,295

'3 Claims. (Cl. 96-106) This invention relates to photographic elements, e.g., films, plates and papers having improved photographic characteristics. More particularly, it relates to photographic film elements having an optically sensitized finegrain, high-contrast silver halide emulsion layer having substantially uniform spectral response throughout the visible region of the spectrum.

Certain combinations of two optical sensitizing dyes which produce a supersensitization effect have been used in photographic emulsions. It is also known to add to silver halide emulsions a combination of three optical sensitizing dyes together with the diazonium pyrazolone dye, flavazine, to produce a panchromatic plate for color photography. These optical sensitizing dyes contain only quinoline nuclei and are pinacyanol, a carbocyanine dye, pinaverdol, as methyl-substituted isocyanine and pinachrome, a diethoxy-substituted isocyaniue. It is further known that many sensitizing dyes, including the abovedescribed quinoline types, leave residual stain in the image layer after processing which has a deleterious affect on the quality of the final image. It is also known that certain combinations of optical sensitizing dyes markedly diminish the sensitizing effect of at least one of the dyes in the combination. In addition to the deficiencies of stain and diminished sensitizing effect, another serious defect is that spectral areas of low sensitivity invariably exist when certain combinations of dyes are used in an attempt to sensitize certain emulsions throughout the desired range of the spectrum. This, of course, results in serious deficiencies in the response of the photographic element to the exposing light. This is particularly true of the silver chloride and silver bromochloride emulsions used in the graphic arts field. These emulsions generally have fine grain and high contrast. However, silver chloride emulsions which have not been sensitized with optical sensitizing dyes have very little sensitivity in the visible region of the spectrum. Their spectral response is generally from the low ultraviolet to 4450 A. Many dyes are available which are powerful sensitizers for these emulsions but generally they sensitize in such a manner that there is an era of very low spectral response between the region of natural sensitivity and the region sensitized by the dye. This usually occurs in the blue region from about 4400 A. to 4900 A.

An object of this invention is to provide improved photographic elements for the graphic arts. Another object is to provide an improved photographic film for the graphic arts industry having substantially uniform response throughout the visible region of the spectrum. A further object is to provide such films which yield images having fine-grain and high-contrast characteristics. Still further objects will be apparent from the following description of the invention.

It has been discovered that relatively high speed photographic films having a panchromatic silver halide emulsion layer can be made by the addition to a silver chloride or a silver bromochloride emulsion of sensitizing amounts of three different types of optical sensitizing dyes, namely,

n 2,920,962 Patented, Jan. 12,

a thiacyanine dye, an oxacarbocyanine dye and a thia carbocyanine dye containing a cyclic hydrocarbon-substituted dioxy ring structure on at least one of the benzene rings of the benzathiazole nuclei.

Suitable dyes of the thiacyanine class which can be used in accordance with the invention are described by Mills in Jour. Chem. Soc., vol. 121, pages 19455-463 (1922), by Fisher and Hamer in Jour. Chem. Soc., vol. 218, pages 2502-2510 (1930), and an improved method for preparing such dyes is described in Kendall U.S.

. Patent 2,310,640.

Suitable dyes of the oxacarbocyanine class are described in Schneider U.S. Patent 2,072,908 and dyes of the substituted thiacarbocyanine types discussed above are described in Anish et a1. Patent 2,423,217, and a related class of dyes similar to those described in the Amish patent contain an alkly substituent on the central methine carbon atom, and are useful in accordance with the invention.

In the preferred aspect of the invention, three specific dyes, one from each of the foregoing classes, are used, namely, l,l'-diethylthiacyanine iodide, 3,3',9-triethyl'- 5,6,5',6'-dicyclohexylidenedioxybenzothiacarbocyanine iodide and 3,3-diethyl-5,6,5',6'-tetramethylbenzoxacarbocyanine iodide. These dyes when used in sensitizing amounts, e.g., 10 to 40 or more mg. per kg. of emulsion ready for coating containing about 6% by weight of gelatin, in gelatino silver chloride or gelatino silver bromochloride emulsions, surprisingly, do not interfere with the sensitizing efiiciency of each other and result in essentially no residual stain in the processed, i.e., developed and fixed, photographic image of the emulsion layer. This combination of three dyes, moreover, provides an exceedingly fast photographic film element which is particularly adapted to the production of direct color separation negatives in lithographic reproduction processes.

The invention will now be further illustrated by but is not limited to the following examples.

Example I A gelatino-silver bromochloride emulsion containing 20 mole percent silver bromide and mole percent silver chloride was made in the usual manner and digested. A photographically active gelatin was used and the emulsion was brought to its maximum sensitivity by addition of conventional adjuvants, e.g., non-optical sensitizing agents. After digestion, there was added to the emulsion, which contained 4.5 moles of silver halide, an ethanol solution of: (1) mg. of the dye, 1,1'-diethyl thiacyanine iodide, (2) 300 mg. of the dye, 3,3,9-triethyl 5,6 5,6' dicyclohexyliden-edioxybenzothiacarbocyanine iodide, and (3) 200 mg. of the dye 3,3'-diethyl- 5,6,5 ',6'-tetramethylbenzoxacarbocyanine iodide. The resulting emulsion wastheu coated onto the gelatin sublayer of the vinylidene chloride copolymer coated polyethylene terephthalate film base of the type described in AlIes and Saner U.S. Patent 2,627,088. The film was exposed, developed, fixed, washed and dried.

With reference to the accompanying drawing which forms a part of this application,

Fig. 1 is an equal energy spectrograph showing the sensitivity of this emulsion.

Fig. 2 is such a spectrograph of the same emulsion sensitized with the same quantities of the latter two dyes but without the 1,1-diethyl thiacyanine iodide being present.

The control film and the test film containing the novel combination of sensitizers were exposed through Wratten No. 47B blue and No. 25 red filters. The exposure ratio of blue to red was 2.29 for the control and 1.59 for the test film. The processed images showed little or no residual stain. A control film was also made in the same manner but 3,3-dietl1yl-9-methylthiacarbocyanine iodide was substituted for the thiacarbocyanine containing the cyclohexylidene substituents. This film, while showing some improvement in speed, showed considerable residual stain in the processed image. i

Example II An emulsion was made and coated in the same way as in Example I but only 85 mg. of the thicyanine dye (1) was used in the sensitizing dye combination. The blue to red filter speed ratio was 1.66 as compared to the control of 2.04. The equal energy spectograph of this photographic film is shown in Fig. 3 of the drawing" and indicates a fairly uniform response throughout the spectral range.

With reference to Example I, the purple dye, 3,3,9- triethyl 5,6,5',6 dicyclohexylidenedioxybenzothiacarbocyanine iodide, was made by the general procedure of Zeh et a1. U.S. Patent 2,068,047, as follows:

-2 g. of Z-methyl-S,6-cyclohexylidenedioxybenzothiazole and 1.53 g. of ethyl p-toluenesulfonate were heated together for 16 hours at from 130140 C., 20 ml. of dry pyridine and 4 ml. of ethylorthopropionate were then added and the mixture was refluxed for minutes. A dark purple color formed and potassium iodide was added in excess. The dye settled out of solution and it was taken up in acetone. Purple crystals separated which were recrystallized twice from alcohol and 0.51 g. purple dye was obtained having a MP. of 273-275 C.

While the invention has been described with respect to gelatin silver halide emulsions, various other waterpermeable organic colloid binding agents for silver halide grains can be used in place of all or a part of the gelatin. Suitable colloids include albumen, casein, alginic acid and the alginates; synthetic colloids, e.g., polyvinyl alcohol, polyvinyl acetals with o-sulfobenzaldehyde, etc.; the methacrylamide/acrylic acid copolymers of U.S. Patents 2,311,548, 2,592,107 and 2,611,763; the 1,2- dithiolanes of U.S. Patent 2,728,668, the copolymers of ShacklettU.S. Patent 2,777,872, etc.

The emulsions may be coated on any type of support or film base, e.g., cellulose esters, e.g., cellulose acetate, and cellulose acetate/butyr'ate; super-polymers, .eg., polyethylene terephthalates, polyethylene terephthalate/isophthalate or polyethylene terephthalate/phthalate, etc., which may have various anchor layers and/or sublayers.

The film supports may be clear or transparent or tinted blue, etc., or may be opaque white by means of an opacifying agent in or on the base.

This invention has the advantage that it provides an improved photographic film for the graphic arts. The film is exceedingly fast and is particularly adapted to the production of direct color separation negatives in lithographic work. The photographic films of this invention yield images of fine grain and high contrast and equal energy spectrographs of the emulsion layers are devoid of areas of low response, that is, there is an equal energy spectral response that is uniform throughout the visible region of the spectrum. A further advantage of the novel films of the invention is that the filter factor is quite low as compared with commercial films for this purpose.

I claim:

1. A photographic film comprising a support bearing a water-permeable organic colloid silver halide emulsion layer containing 1,1'-diethyl thiacyanine iodide, 3,3,9- triethyl 5,6 5,6' dicyclohexylidenedioxybenzothiazole carbocyanine iodide, and 3,3-diethyl-5,6,5,6-tetramethyl-benzoxacarbocyanine iodide.

2. A film as set forth in claim 1 wherein said colloid is gelatin.

3. A film as set forth in claim 1 wherein said silver halide is silver bromochloride.

References Cited in the file of this patent UNITED STATES PATENTS 1,383,620 Friese-Greene July 5, 1921 2,072,908 Schneider Mar. 9, 1937 2,423,217 Anish et a1. July 1, 1947 FOREIGN PATENTS 651,451 Great Britain Apr. 4, 1951 OTHER REFERENCES (COPY 

1. A PHOTOGRAPHIC FILM COMPRISING A SUPPORT BEARING A WATER-PERMEABLE ORGANIC COLLOID SILVER HALIDE EMULSION LAYER CONTAINING 1,1''-DIETHYL THIACYANINE IODIDE, 3,3'',9TRIETHYL 5,6 - 5'',6'' -DICYLOHEXYLIDENEDIOXYBENZOTHIAZOLE CARBOCYANINE IODIDE, AND 3,3''-DIETHYL-5,6,5'',6''-TETRAMETHYL-BENZOXACARBOCYANINE IODIDE. 